Miyazono S, AA Pease, TB Grabowski, & SR Fritts. 2019. Recruitment dynamics and reproductive ecology of Blue Sucker in Texas, with a focus on the Big Bend region of the Rio Grande. U.S. Department of Interior, Fish and Wildlife Service, Cooperator Science Series XXX-XXX. Washington, D.C.
Blue Sucker (Cycleptus elongatus) is a state-listed threatened species in Texas and is considered vulnerable throughout its range. Once considered a single, wide-ranging species, blue suckers are now recognized as a complex of closely related, but genetically and morphologically distinct species within the genus Cycleptus, including an undescribed species within the Rio Grande Basin. Numerous factors likely are driving the decline of blue suckers in Texas, including flow alteration, water quality, habitat fragmentation, and changing land-use patterns, but it is not clear how these factors interact to influence the abundance and distribution of the species. Our research integrates a variety of methodologies to provide information critical to the conservation and management of Blue Sucker in the Sabine River (Texas and Louisiana) and Colorado River (Texas) and Rio Grande Blue Sucker (Cycleptus sp. cf. elongatus) in the Rio Grande. The objectives of this report are to 1) determine the habitat associations of the young-of-the-year (YOY) Rio Grande Blue Sucker; 2) assess the effects of flow regime on growth and recruitment of Blue Sucker in the lower Sabine River; and 3) examine differences in life-history traits of Blue Suckers and flow regime across river basins in Texas. This study is the first to quantitatively address the sequence of YOY blue sucker mesohabitat use and increases our understanding of early life history of blue suckers, and the results of this work will help to develop conservation and management strategies (e.g., prioritizing conservation areas, developing flow recommendation, etc.) for blue suckers throughout their geographic distribution. Key findings of this study were: 1) The body size of YOY Rio Grande Blue Sucker in pool habitats were significantly lower than that in other mesohabitats, suggesting that YOY Rio Grande Blue Sucker undergo onotogenetic habitat shifts into higher current velocity habitats as they grow. 2) Slow current areas, such as pools, could be important nursery habitats for small YOY Rio Grande Blue Sucker (total length ≤ 45 mm). 3) YOY Rio Grande Blue Sucker move into riffles and runs as they grow from April to June, suggesting that extreme low flow conditions during early summer may negatively affect the habitat quality or availability for YOY Rio Grande Blue Sucker. 4) The growth and recruitment of Blue Sucker in the lower Sabine River increased with increasing the river discharge from early summer to fall in our study areas. 5) The life-history traits of Blue Sucker differed between the lower Sabine River and the lower Colorado River: the total length and age of Blue Sucker in the lower Colorado River were larger than those of Blue Sucker in the lower Sabine River, and the growth and mortality rates of Blue Sucker of the lower Sabine River tended to be higher than those of the lower Colorado River. 6) Our results suggest that mesohabitat area and flow regime could be important factors determining the growth and recruitment of blue suckers, and the importance of these environmental factors could change according to the life-history stage (larval stage, juvenile stage, and adult stage). 7) Important areas for future research efforts include a) quantifying the differences in the mesohabitat area/quality/density among the three river basins; b) examining interactions between the spatial distributions of potential spawning habitat relative to suitable YOY mesohabitat and how variations in river flow influence their quality and connectivity to each other; and c) continuing to monitor the effects of flow regime on blue suckers for longer time periods.